Electrical – mildly charged wall
(This folder seems to have become the defacto electrical question depository, so will try here rather than “General”.)
A wall between two bedrooms in my house seems to have become slightly energized. When I hold my Greenlee voltage detector a few inches away or touch the wall with it, the detector lights up like a christmas tree. I have no idea how long it has been this way, could have been since it was built, I guess. I just happened to discover it when I was idly playing with the voltage detector.
The question is: what is the best way to locate an area where a bare sot of an electrical cable may be touching a wall. (Unless someone has an alternative explanation.) I can localize the problem spot to some excent by how far away from the way I can hold the voltage detector and still have it light up. Unfortunately, this still gives me an area about four feet in diameter. Is there any way to zero in on a damaged cable? I hate to rip up any more drywall than necessary.
The house is a 1957 ranch with two conductor Romex cable with no ground. I have discovered other areas with splices buried in the wall, so that could be the case here. Splices are with the wires twisted and soldered and then taped. Certainly not at current code levels…
Thanx
Replies
My guess would be that the house is fine and the detector is bad (too sensitive.
None of the other walls in the house give this type of reading. To test for voltage on a standard outlet receptical, I usually have to touch the hot wire to get a reading. I doubt that the voltage detector is more sensitive than other such testers. After I posted, I also tried my Zircon Multiscanner Pro, and it also gave about the same results (although it is difficult to get consistent results with the multiscanner). Ithink I have narrowed the spot of highest voltage down to an area less than 6" square, so I am about to start cutting wallboard. I did it by scanning with the Greenlee tester held progressively further from the wall so I only got an indication in a fairly small spot. I was pretty much able to verify that spot with the Zircon by setting the reference spot of the Zircon within the charged zone of the wall, so that only higher voltages were detected. I will report back when I have dissected the wall, as I know all of you are waiting with baited breath for the outcome...
I wouldn't be surprised if there's a splice buried there, or possibly even some K&T stuff. Basically, the hot and neutral wires in some circuit are probably separated by some distance, or the neutral is disconnected but the hot isn't. It doesn't mean that the bare wire is touching the wall -- that wouldn't cause your readings unless there's some sort of metallic lath or some such used in the construction.
This isn't inherently dangerous, other than the "normal" dangers associated with improper splices.
Before you start exploratory demolition, what's in the room near the wall, or on the other side of it? Non-contact testers are very sensitive to radio frequency, so if there's some kind of wireless device on the other side of the wall, that could be what trips it an a distance of a few inches, whereas 60 Hz AC requires it to be much closer. Test the same spot on the other side of the wall before you open it up.
-- J.S.
John -I turned off everything in the area and even all other circuits. I originally thought it was probably induction from the high power lines that run along the street about 20 feet away. However, the wall closest to the powerline did not give me a reading and since I have narrowed it down to a spot about 4 inches in diameter that is about five feet from the floor and in the area where the Romex comes down that wall from the attic, I think it most likely is a bad splice. I did turn everything off in the house except for that one circuit, from which everything was unplugged, and found that the electric meter did not budget for the several minutes of the test. I thus assume it is a pretty negligible leakage. However, I still won't feel right about it until I fix it...
I wonder if you have foil backed DW. I ran into in a house of that vintage. But it had been remodeled so I have no idea if it was orginal or not.That along with a hot wire and no neutral or bad splice with the hot against the foil might give you such simptoms..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Those non-contact sensors look for voltage, not current. They're not like a clip-around ammeter. It doesn't necessarily have to be a splice, but that's a good possibility. Do check the outside first, and see if there's anything unusual at that point. The 4" diameter leads me to suspect a buried box with no cover -- high for a switch, but possibly a sconce? Does the wall look patched either inside or out?
Nice mystery, thanks for sharing it.....
-- J.S.
What the non-contact sensors really look for is the electrostatic field. When two oppositely-charged wires are close together the electrostatic field remains tightly confined between them, but when the wires are farther apart the field spreads out. This field we're talking about is similar to but not exactly the same as what you see when iron filings are sprinkled on a piece of paper above magnets, and it spreads out in arcs the same way.The non-contact sensor can detect this field and will flash/beep/whatever when the field is stronger than a certain level.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
Just curious if it is possible someone nailed or screwed a hot lead when drywalling and get a reading like that. Like I said, just curious.
Yeah, that could happen -- put a DW nail through a piece of romex, eg, and the area right above the nail would "light up". But the area would be fairly definite -- you could pretty much identify the precise location of the nail.Keep in mind that how much the field spreads out varies based on distance. If the "hot" spot is near the surface (as with the nail) then the the detector will zero in on the spot. If the "hot" spot is deeper in the wall (and especially if it's not a "spot" but a length of wire) then the detector will light up for a much larger area.This ability to detect "tight" vs "diffuse" fields will, however, vary with the type and quality of the detector.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
Thanks for the education. I appreciate it.
The walls are probably plaster but do you know if metal screen was used instead of rock lath or wooden lath? If the ground (metal spiral sleeve) lost contact in a box en route to that wall's boxes, the wall could become hot of a device was replaced and proper polarity wasn't observed.
The walls are 1/2 drywall on 2x4 studs. There appears to be no patch on the wall at this point. The field seems to be equally strong on either side of the wall, and with the Greenlee voltage detector, seems to give an indication of an area about six feet in radius if I touch the wall with it or about six inches away from the wall at the "hot spot". The "hot spot" is about a foot away from a door and touching the door with the Greenlee also gives an indication of voltage. I have not yet had a chance to open up the wall and probably won't for a couple of days. I have opened up other walls and none of them have any metal mesh or lath in them, just standard issue drywall. Thanks for the ideas. I will report back when I get a chance to whack a section out of the wall.
OK, I guess I need to go find my dunce cap... I haven't opened up the wall but I think I have a pretty good idea what the situation is. I haven't lived in the house for a while, so I forgot that the receptical along that wall is switched from a wall switch on the other side of the door, so the stray voltage occurs along that electrical wire. I checked on another bedroom with the same switching arrangement and it is the same situation. So I am pretty sure that most of the voltage comes from the fact that there is a hot wire to and from the switch without a counter balancing neutral. I don't know why I there is one spot that seems somewhat "hotter" than the rest, but I ain't gonna worry about it no more...
Thanks for all who pitched in.
Yeah, the switch leg would read "hot" when the light is on. Should "cool off" when the light is switched off. This is the one case where you don't have a neutral to "absorb" the stray electrical field.If the wire contained a ground you likely wouldn't see this effect, but likely you have romex without ground.
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
(PS: To "cool off" the wire you need to plug a lamp or other "load" into the receptacle, in addition to switching the switch off.)
Half of the harm that is done in this world is due to people who want to feel important. They don't mean to do harm but the harm does not interest them. --T.S. Eliot
No, you'd only need the cap if you actually busted the wall open. ;-)
The hot spot is probably nothing more than a bend in the romex that brings it closer to the drywall. Like Dan says, plug in an incandescent, turn it off at the wall switch, and check again.
I really hate when I demo something only to find out that -- duh -- it was all a mistake.
-- J.S.